Mercury is a heavy metal with extreme toxicity, the ability to biomagnify, and long range atmospheric transport of its gaseous form. Past and present industrial uses of mercury have resulted in the pollution of soils, groundwater, rivers and marine ecosystems worldwide, the clean-up of which, using standard technology, is either not feasible or is prohibitively costly. A low cost and environmentally friendly alternative is bioremediation: the use of microbes or plants (phytoremediation) to remediate contaminated sites.

In this timely book, established mercury experts review the latest research in this area, including the genetic engineering of bacteria and plants. The gap between laboratory research and field application is bridged using case studies: An abandoned chlor-alkali electrolysis factory in Kazhakhstan, a former PVC plant in Albania, and the Madeira River Basin in the Amazon region. The remaining chapters cover: the mercury-cell process of the chlor-alkali electrolysis industry; a pilot plant for wastewater bioremediation; and a comparison of the efficiency of microbial bioremediation to clean-up three types of industrial wastewater. The book covers the complete range from laboratory scale research to full scale industrial operation and shows a multitude of options for future mercury bioremediation technologies.

Essential reading for research scientists, graduate students, and other specialists interested in mercury bioremediation, the book is also recommended reading for environmental microbiologists, chemists and engineers.

Table of contents

1. Current Research for Bioremediation of Mercury

Irene Wagner-Döbler

This review covers approximately the last ten years of research. It is based on appr. 150 publications on mercury remediation in Medline, including 83 citations of our papers from 1999 and 2000 (von Canstein et al., 1999; Wagner-Döbler et al., 2000a). After eliminating citations which were not directly related to the topic, roughly 120 references remained. Completeness is not claimed by this review, and I apologize for work that may have been over-looked or not been thoroughly appreciated. Many reviews on metal or mercury bioremediation have been published during this period and provide additional information (Nascimento and Chartone-Souza, 2003; Doty, 2008; Eapen and D'Souza, 2005; Kramer, 2005; LeDuc and Terry, 2005; Meagher and Heaton, 2005; Miretzky and Cirelli, 2009; Ruiz and Daniell, 2009; Wagner-Dobler, 2003; Nascimento and Chartone-Souza, 2003; Lloyd and Lovley, 2001; Lloyd et al., 2003; Lovley, 2003; Means and Hinchee, 1994; Pan-Hou, 2010).

In 1975, a mercury cell chlor-alkali facility in Pavlodar, Kazakhstan began operations. This facility is located at the Pavlodar Chemical Plant (PCP) and began operations when mercury cell technology was at its peak in the former USSR. For a number of reasons, this plant had the highest rate of mercury use among similar designs (estimated at 1500 g of mercury per ton of caustic soda produced). After the collapse of the USSR in 1992, the facility was shut down. Despite a poor economy, scientists, PCP administrators, local environmental NGOs, regional authorities, and local politicians of Kazakhstan persisted to reduce mercury contamination that was inherited from the former USSR military-industrial establishment. Due to financial support from the European Union (EU) and the United States (i.e. U.S. Environmental Protection Agency) as well as contributions from Ukrainian scientists, field research was conducted. This research consisted of comprehensive monitoring of the atmosphere, soils, surface water and groundwater to determine the environmental risks posed by localized mercury 'hotspots' that occurred from mercury cell production losses of about 1310 tons of metallic mercury. The mercury clean-up project was distinguished by its unprecedented transparency. Good awareness of the problem, interest of all parties involved in the project and participation of highly qualified specialists and the use of simple and cost effective technologies allowed minimizing the principal risks (mainly for the Irtysh River and communities in the northern outskirts of Pavlodar) at a cost of approximately $ 16 million by the government of Kazakhstan. Past data and archive materials of the PCP and its production history included: environmental monitoring results, risk assessment variants of the demercurization design, and remediation progress. Post-demercurization monitoring was also conducted after completion of clean-up activities to assess the efficiency of the remediation and residual risks and also to make suggestions on further improvement of the environmental situation.

North of Vlora in Albania is the site of a former chemical manufacturing complex consisting of a chlor-alkali factory and plants for the production of vinyl chloride monomer (VCM) and polyvinylchloride (PVC). The factory closed in 1992 and was completely destroyed during a civil uprising in 1997. It covers an area of approximately 1 km2 located directly at the coast of the Adriatic Sea. The major environmental problems are the destroyed mercury cells of the chlor-alkali electrolysis plant, the waste-water which has been discharged into the Bay of Vlora without treatment in the past, and the sludge from the former production processes which was dumped in the area between the plant and the Bay. Hydrological, geochemical and geophysical investigations showed that mercury concentrations in ambient air exceeded the emission limit of 50 ng m-3 in about 40% of measurements; the maximum was reached with 50 µg m-3. The soils were found to be contaminated only within the unsaturated zone. Here the maximum mercury concentration was greater than 20,000 mg kg-1. The mercury distribution in marine deposits of the Adriatic Sea did not indicate any influence of the discharged waste water. A significant contamination hot spot was the electrolysis building. Here, mercury concentration was higher than 60,000 mg kg-1. Most of the mercury was present in elemental form. Therefore the impact of mercury pollution in the Bay of Vlora on humans and indicator organisms was small.

4. Land Use Change and Mercury Mobilization in the Amazon: The Madeira River Basin Case Study

L.D. Lacerda and W.R. Bastos

Mercury is an ubiquitously presence in large areas of the Amazon, resultant form the gold rush which occurred in the region during the past century and from emissions of colonial mining operations, which used Hg amalgamation as major mining procedure. High Hg environmental levels are also favored by the capacity of most Amazon soils to accumulate and immobilize atmospheric Hg deposition over millennia. The immobilization of Hg, however, depends on the integrity of the ecosystems functioning, directly influenced by the recent development of the region. The effect of land use change on Hg mobilization from Amazon soils and sediments to the atmosphere and waterways is discussed, based on decadal data on Hg distribution in soil profiles under different land use categories; primary tropical forest, slashed forest prior to burning, silviculture and pastures. Degassing rates from these soils were monitored under different sampling periods, as well as air Hg concentrations over them. Comparisons of the Hg distribution in water, suspended solids and bottom sediments along a 1,600 km stretch of the Madeira River obtained in 5-years interval cruises are also discussed in view of large scale changes in the basin. All the results suggest strong mobilization of deposited Hg, both to the atmosphere and waterways. This process is suggested as responsible for the maintenance of elevated Hg concentrations in top carnivorous fish and riverside human populations reported recently, even after a decade of the cessation of Hg emission from gold mining in the region.

5. Mercury in the Chlor-alkali Electrolysis Industry

Pawel Gluszcz, Katarzyna Fürch and Stanislaw Ledakowicz

This report is based on all publicly available information sources, technical reports and analyses of international consortia. Its task is to provide up to date data on chlor-alkali plants, in particular those using the mercury cell process, in the most comprehensive way. Except the global analyses of chlor-alkali industry some fundamental knowledge about the mercury (amalgam process) cell technology is provided. The situation in chlor-alkali industry has changed significantly within last ten years, mostly due to new regulations of the European Parliament and Council, as well as of activities undertaken within the UNEP Global Mercury Partnership. Membrane technology now represents more than the half (51.2%) of the installed production capacity of Euro Chlor members. The mercury process accounts for 31.8% at the beginning of 2011, continuing the progressive phase out of this technology. The diaphragm process still accounts for a bit less than 14% of the total capacity. The number of plants and the mercury cell-based production capacity continue to show a world-wide decrease: the number of plants went down from 91 to 57 over the period 2002-2010 (-37%) and the mercury cell-based capacity from 9.1 million tonnes to 5.5 million tonnes (-40%). The World Chlorine Council (WCC), which represents about 85% of global mercury-based chlorine production, has provided a regionally-based report on mercury consumption and emissions showing declines in mercury emissions from about 23.3 metric tonnes per year in 2002 to 6.4 metric tons per year in 2009. Global mercury emissions have been further substantially reduced in the period 2002-2010. They went down from 24.6 Hg tonnes/year to about 6.7 Hg tonnes, or 73% decrease over the eight years of reporting by WCC. Forty-two mercury-based chlorine plants in Europe remain to be voluntarily phased out or converted to non-mercury technology by 2020. In 2010, emissions for all mercury cells across Europe reached an all-time low of 0.88 grammes Hg per tonne of chlorine capacity, while the average mercury emissions for Western European countries remained at about 0.76 g Hg/t Cl2; capacity. The chlor-alkali companies operating mercury-cell plants have voluntarily agreed to phase out the technology by the year 2020.

6. Long-term Operation of a Microbiological Pilot Plant for Clean-up of Mercury Contaminated Wastewater at Electrolysis Factories in Europe

A plant for BIOlogical MERcury Remediation (BIOMER) based on mercury resistant bacteria was operated for three years at a chlor-alkali factory in technical scale. Here we report on the performance of the plant and on the technical problems that had to be solved until a stable and continuous operation could be guaranteed. One basic improvement was the installation of a pre-treatment unit. Basic process characteristics were determined during long-term operation. The BIOMER plant could treat wastewater with up to 10 mg/L of mercury. The optimal operation temperature was between 25-35°C. A salt concentration of up to 40 g/L of chloride could be tolerated by the microbes, but the fluctuations should be as small as possible. The bioreactor has to be operated at a pH of 7.0 ± 1.0. A space velocity of up to 4 h-1 could be obtained. The wastewater flow rate should be constant to avoid export of fine particles. Finally a space time yield of 1 kg mercury per day and m3 bed volume corresponding to 100 m3 wastewater per day is possible. The biological system showed a high capacity for self-regeneration. Interruptions of the water inflow for up to 12 hours and of the medium supply over several days were tolerated. Toxic shocks loads of high concentrations of chlorine or mercury chloride also caused only a transient reduction of the microbial activity. The plant was able to quickly return to normal operation with high mercury retention efficiency after such stresses. The results from the long-term operation show that a process can be scaled up from laboratory tests to an industrial plant without any serious engineering problems. It was demonstrated that the BIOMER plant is able to work under industrial conditions at two different chlor-alkali electrolysis factories in Europe.

7. Microbiological Treatment of air Scrubber Solutions From a Waste Incineration Plant and Other Mercury Contaminated Waste-Water: A Technology in Search of an Application

Johannes Leonhäuser, Wolf-Dieter Deckwer and Irene Wagner-Döbler

A microbiological treatment system comprising three consecutive stages of packed bed bioreactors inoculated with mercury reducing bacteria was operated in laboratory scale. The efficiency of this system for removal of mercury from the following types of industrial wastewater were determined: (1) chlor-alkali electrolysis; (2) gas scrubber solutions from the waste incineration plant TAMARA; (3) gas scrubber solutions from incineration of various types of waste from a chemical factory. The data show that all three types of wastewater could be efficiently cleaned. Factory wastewater with mercury concentrations of up to 460 mg/L had to be diluted to obtain a mercury concentration < 10 mg/L. Treatment efficiency was reduced by chloride concentrations above 39 g/L or toxic compounds, which were present in one of the wastewater batches from the chemical factory. The sandfilter buffered transient changes in the bioreactor efficiency. The activated carbon filter functioned as a polishing step so that effluent concentrations below 50 µg/L could always be maintained. The best and most stable bioreactor performance was obtained for electrolysis wastewater, which has a relatively predictable composition.